In recent years, an apparatus is known which utilizes thermal energy obtained by collecting sunrays as clean energy which will not affect the environment. As the above-described apparatus, there has been developed a solar concentrating heat receiving system (hereinafter, referred to as a concentrating heat receiving system which converts thermal energy obtained by collecting sunrays to electrical energy to generate power (refer to Patent Document 1, for example).
In the above-described concentrating heat receiving system, sunlight and heat are normally collected by a combination of a heat receiver and a sunlight collecting apparatus in which mirrors are used. As the above-described combination types of the sunlight collecting apparatus with the heat receiver, there are in general two types available, that is, a trough-type light collecting system and a tower-type light collecting system.
In the trough-type light collecting system, a half-cylindrical mirror (a trough) is used to reflect sunrays to collect sunlight and heat in a pipe passing through the center of a cylinder, thereby raising the temperature of a working fluid which passes through the pipe. However, the trough-type light collecting system is subjected to uniaxial control in which the mirror turns so as to follow sunrays and, therefore, cannot be expected to significantly raise the temperature of the working fluid.
On the other hand, the tower-type light collecting system is provided with a concentrating heat receiver placed above a tower unit which is erected from the ground and a plurality of reflection light control mirrors for collecting sunlight which is referred to as heliostats are placed so as to surround the tower unit, thereby guiding sunrays reflected by the heliostats into the concentrating heat receiver to collect sunlight and heat. In recent years, in view of further enhancing a power generation cycle, there has been actively developed a concentrating heat receiving system which is a tower-type light collecting system where the concentrating heat receiver can be used to conduct heat exchange, thereby increasing the temperature of a working fluid to a greater extent.
For example, as shown in Patent Document 2, a concentrating heat receiver used in a tower-type light collecting system is provided with a casing having an opening portion into which sunrays are made incident, and a heat receiving portion which receives sunrays made incident into the casing. Further, the heat receiving portion is provided with a plurality of heat receiving pipes which extend along an inner circumferential face of the casing, a low-temperature side header are collectively connected to one ends of the plurality of heat receiving pipes, where one ends are the upstream side of the heat receiving pipes in relation to a flowing direction of a working fluid, and a high-temperature side header are collectively connected to the other ends of the plurality of heat receiving pipes, where the other ends are the downstream side of the heat receiving pipes in relation to the flowing direction of the working fluid.